The term "biodiversity" was derived from "biological" and "diversity," and refers to the total diversity of all life in a given locale - one as small as a backyard (or smaller) or as large as the entire planet Earth. One example of a biodiversity measurement is bird watchers listing the species they see in an area on a given day. Although it is often thought of as the number of species in a locale, biodiversity actually has a much wider definition and encompasses levels above and below that of the species. Wilson described biodiversity as the "totality of hereditary variation in life forms, across all levels of organization, from genes to chromosomes within individual species to the array of species themselves and finally at the highest level, the living communities of ecosystems such as forests and lakes." 2

There is a strong and growing consensus among environmental biologists that we are currently in the midst of a biodiversity crisis. Human-induced global climate change is now accepted as fact. Habitats are rapidly disappearing. Species are going extinct at accelerating rates.

Why should we care about preserving biodiversity? Environmental biologists have outlined two general reasons. First the utilitarian reasons: We rely on a large number of animal, plant, and fungal species for various purposes including food and medicine. In fact, as Simon Levin notes, about forty percent of "all prescription drugs in the United States contain active ingredients originally derived from nature."3 Moreover, our current knowledge is probably akin to the tip of an iceberg compared to the potential medicinal or other benefits from species that remain undiscovered. This is particularly true with respect to microbes and fungi, which we know less about than plants and animals.

In addition to the benefits from individual species, humans also benefit from maintaining healthy ecosystems; perturbing these ecosystems can adversely affect human health. For instance, Lyme disease emerged in the northeast United States because of changes in the forest ecosystem of that region. As the forests became more fragmented, population sizes of white-footed mice soared because they were now free from competitors or predators, whose populations had declined in the now patchy forests. The mice are a source of blood for ticks, which can carry the Lyme-disease bacterium. As the diversity of other small, ground-dwelling rodents decreased, the mice became an increasingly exclusive source of food for ticks, which also feed on humans and other mammals. This resulted in a surge in the exposure of humans to the bacteria. Through a series of links, forest fragmentation has permitted Lyme disease to rapidly become a major health problem in the eastern United States. (See the Microbial Diversity unit.)

In addition to the utilitarian reasons, there are also non-utilitarian reasons to preserve biodiversity. Part of the beauty of nature comes from the copious diversity of life. Most would agree that a marked reduction in the Earth's biodiversity would make it a much poorer planet. Related to both the utilitarian and the non-utilitarian reasons is that biodiversity is essentially irreplaceable. The creation of new species by the natural process of speciation usually occurs in time spans of many thousands of generations, far exceeding human lifetimes. The biodiversity that disappears on our watch will be lost not only for our children and their children, but will remain lost for countless generations to follow. In human terms, extinction is forever. Is it moral for humans to cause the irrevocable loss of other species if we can avoid it?

The line between utilitarian and non-utilitarian reasons for preserving biodiversity is blurred. Some reasons now listed as "non-utilitarian" may actually turn out to be utilitarian. Recent research is starting to give us hints that as diversity collapses, the whole ecosystems on which we depend may collapse on a global scale as well. The loss of diversity from a particular area may have a more drastic consequence than simply "it's not pretty anymore" - it may come to mean, "this is now a wasteland of biological life."